Scientists Examine Temperature History of Global Coral Reefs

Findings shed light on ocean temperature patterns that cause coral bleaching, as well as factors that may make some reefs more resilient to climate change.

The ongoing third global coral bleaching event, which started in 2014, is just the latest in a pattern of warmer ocean temperatures that stress coral reefs. A recent study published in Nature's Scientific Reports confirms this, identifying temperature trends in historical data records from 1985-2012. This information sheds light on the patterns associated with the frequency and timing of stress events likely to result in coral bleaching.

Scientists with NOAA Coral Reef Watch examined worldwide sea surface temperature trends and variability at the reef-scale using satellite data. They found that among over 60,000 reef locations globally, 97 percent showed warming. The analysis also determined coral bleaching was three times more likely in recent times than at the beginning of the record in the late 1980s.

According to the study's lead author, Scott Heron, "The increase in temperature and stress events on coral reefs is a stark example of the effects of climate change, impacting an ecosystem that provides habitat to over one quarter of all marine fish species and many other animals, as well as livelihoods and coastal protection for over 500 million people around the world."

In addition to mapping historical changes, the analysis can also help scientists identify reefs with greater ability to survive as temperatures warm, increasing their value for conservation efforts. Understanding where these 'bright spots' are located is critical given the global coral bleaching event that is still underway and the predicted increases in bleaching for the coming decades.

Histogram of bleaching-level thermal stress events, 19852012.
Percentage of global reef pixels affected by bleaching-level thermal stress, 1985-2012. Seven-year averages showed a three-fold historical increase, a trend that is predicted to continue in the future. Credit: Heron et al., 2016

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